I am not a game developer, but I do program. When I think of motion controls, good near 1:1 motion controls, the thing I imagine would give me a headache is animations. Developers are used to having a few set animations for a character. They even bring in stunt people and sports stars to try to get the animations lifelike. Not only does that improve the look of the game, it makes development easier. If I can focus just on a finite subset of movements, my scope is more manageable.
Now with motion controls (especially Natal) that mode of thinking is gone. I have to program my characters to be able to do almost anything. I must think about the skeletal structure of my character and their clothes, and I must do it in real time while concurrently determine the player's motion and render HD textures.
"You can never jump away from Conclusions. Getting back is not so easy. That's why we're so terribly crowded here."
Canby - The Phantom Tollbooth
